The invention concerns a device for measurement of loose mixtures components content, particularly for determination of the content of incombustible materials in the dust zones of mine workings and for dust hazards in mines.
Well known is, for instance from Polish description of the applied model No. 27017, a device for determination of solid incombustibles in dust zones, consisting of a beta radiation source and a scintillation probe recording backscattered radiation at the dust sample. Application of the scintillation probe as the radiation detector calls for high voltage supply, which makes intrinsic safety impossible to be guaranteed and eliminates it from its usage underground.
Well known is also, for example from Polish description of the applied model No. 30100, a device serving this purpose, equipped with a semi-conductor detector of backscattered beta radiation at the dust sample. It significantly limits power consumption and enables the application of intrinsically safe electric circuits. However the fact that the radiation source, the sample container and the detector are, as in the previous case, separate elements, exposed to shocks and mutual shifting causes the instability of indications in coal mine conditions.
Similar faults can be found in the solutions well known from foreign literature, for example the Australian device described by C. R. Ailwood, K. Bunch, R. A. Grawitis and I. S. Watt in which a loose mixture sample container and a scintillation probe with a photomultiplier as the detector, constitute a mechanically combined system which does not guarantee stability even at weak shocks. The photomultiplier applied in the probe is very fragile and both the supplying circuit and the current intensity meter are separate instruments joined by cable to the device, which causes difficulties in its use underground. Furthermore, employed in this device is a gamma 238 Pu radiation source with activity 30 m Ci which requires a special type of protective screens. Required sample mass of 25-30 g is very high, too. An American solution PERO has the same faults and disadvantages.
The above described devices for the measurement of content of loose mixtures components, consisting of a radiation source and a scintillation probe or a semi-conductor detector are usually equipped with a battery, a wide-band charge amplifier, an integrator and a indicator. Very long response time and low shock resistance of the indicators are the main faults of such solutions which are particularly inconvenient in coal mine underground conditions.
Well known are also devices for the measurement of content of loose mixtures components equipped instead of the integrator and the indicator with an electronic pulse scaler controlling the digital display by the decoder. These devices have an advantageous, 2.5 times shorter response time than the indicator and furthermore, they are shock-resistant. The main fault of these devices is that they do not indicate directly but they require calibration. There exist a significant difficulty in constructing a device with the direct digital read-out. This difficulty results from the stochastic character of pulse appearance, the mean amount of which at a given time represents the content of the components and from the great amount of surrounding noise, changing accordingly to a given specimen of the detector and the radiation source, a zero level value and transducing sensitivity. These factors cause difficulties in ensuring, from the service point of view, easy calibration of the device to the measurement of dust components content with the direct digital read-out.